Electronic device and method of manufacturing same

ABSTRACT

The electronic device ( 100 ) comprises a body ( 20 ) with a cavity ( 30 ) wherein a semiconductor element ( 10 ) and a thermally conductive layer ( 33 ) are present. The cavity ( 30 ) is filled with an encapsulation ( 35 ) of an electrically insulating material wherein contact faces ( 47, 48 ) are mechanically anchored.

The invention relates to an electronic device comprising a body having acavity with an inner side and an aperture, a semiconductor elementprovided with contacts, which semiconductor element is present in thecavity and at least part of its contact are situated in the aperture ofthe cavity.

The invention also relates to methods of manufacturing an electronicdevice comprising a body having a cavity with an inner side and anaperture, and a semiconductor element provided with contacts, whichsemiconductor element is present in the cavity and at least part of itscontacts are situated at the aperture of the cavity.

Such a method and such a semiconductor device are disclosed in U.S. Pat.No. 6,087,721. The known semiconductor device comprises a thermallyconductive layer on which a body of insulating material is provided. Abipolar transistor is present that serves as the semiconductor element.This transistor has all its contacts in the aperture. On the side facingaway from the aperture, the transistor is placed on a conductivesurface. This surface is in contact with the thermally conductive layervia a preferably thermally conductive intermediate layer.

A drawback of the known semiconductor device resides in that thecontacts must be connected to bonding wires. With a view tominiaturization it is desirable to substitute bonding wires with metalor solder bumps. If further elements are present, it must be possible,however, to connect the semiconductor element to said further elements.

Therefore, it is a first object of the invention to provide asemiconductor device of the type described in the opening paragraph,which can be placed on a carrier by means of solder or metal bumps.

Said object is achieved in that the contacts are in electric contact,via conductive connecting pieces, with contact surfaces, which contactsurfaces are anchored in electrically insulating material. In the deviceaccording to the invention, contact surfaces are provided as islands andbridges in the electrically insulating material, which also serves as anadhesive material for these contact surfaces. The contact surfaces arepresent in a plane that is parallel to the cavity, yet extendssubstantially outside said cavity. In this manner, the device can beplaced on a carrier by means of solder or metal bumps or in a similarfashion.

It is a first advantage of the invention that the contact surfaces canbe very close to the contacts, which is not possible if use is made ofleads or bonding wires. In this manner, losses at higher frequenciescaused by self-inductance of the leads or the bonding wires areminimized.

It is a second advantage of the invention that it can also be embodiedso as to have small dimensions. The size of the contact surfaces can bechosen to be much large than that of the contacts to make sure thatsufficient current is supplied and to be in keeping with the placementaccuracy on the carrier.

In a first embodiment, the body comprises an electrically insulatingmaterial which encapsulates the semiconductor element with the exclusionof the aperture. In fact this body is nothing more than thesemiconductor element, or an array thereof, that is provided with anencapsulation. Such encapsulation may be realized by providing the oneor more semiconductor elements with their contacts on a temporarycarrier, molding so as to provide the encapsulation and removing thetemporary carrier. The important advantage hereof resides particularlyin the embodiment with more than one semiconductor and other element:the contact surfaces will then be provided with electrically conductiveinterconnects to interconnect the semiconductor devices according to adesired pattern. Suitable combinations of semiconductor elements includesemiconductor elements on the basis of different substrates, such assilicon, GaAs, GaN and InP; other elements such as magnetoresistivesensors, microelectromechanical elements (MEMS), bulk acoustic wavefilters and the like.

In a second embodiment, the electrically insulating material forms anenvelope, which also fills the cavity. In this manner the insulatingmaterial also adequately encapsulates the semiconductor element. Anadditional protective layer can thus be dispensed with. As a result,there is greater freedom as to the choice of the body surrounding thecavity. The body may be of a polymer material, but glass or ceramic arealso possible. It may alternatively be a multilayer substrate comprisingcomponents and conductors. The use of glass has the additional advantagethat the cavities can be adequately manufactured at low cost by means ofpowder blasting.

In a favorable embodiment, a thermally conductive layer is present whichis in thermal communication with the semiconductor element and which isat least partly situated on the inner side of the cavity. In this mannerheat dissipation is guaranteed. This is particularly important in thecase of power elements. If a conventional bipolar transistor is used,the thermally conductive layer can be used as a connection for thecollector-electrode. The thermally conductive layer is then guided tothe first side where it contacts a contact surface. Favorably, thecontact surfaces, which are present on a substrate, are integrallyassembled with the other part of the device.

In a further embodiment, the thermally conductive layer may cover onlypart of the inner side of the cavity. This embodiment is particularlysuited for semiconductor elements having all contacts at the aperture,such as integrated circuits, field effect transistors. This isfavorable, in particular, in combination with a body with internalconductors. In this case the thermally conductive layer in factcontinues through the substrate, thereby also enabling conductiveconnections with the side of the device facing away from the aperture.

In a different embodiment, the device comprises further components whichare connected, as desired, with contacts of the semiconductor element byelectroconductive tracks (i.e. interconnects). Such components can beaccommodated in separate cavities of a desired size and depth, but theycan alternatively be assembled on the body or provided using thin andthick film processes. It is additionally possible that some componentsare present in the cavity itself. The electroconductive tracks can bearranged in the body. The tracks can also be connected to the contactsurfaces. The device then has connection points in another, suitableposition. Examples of such components are passive components, such asresistors, coils, capacitors and transformers; high-frequency componentssuch as resonators, strip lines, couplers, switches; and sensors.

The semiconductor component preferably is a transistor. Transistors canvery suitably be used as power amplifiers. In a device having such atransistor it is required that the contacts are present on a side, thatheat is properly dissipated, that the height of the device is small, andthat the device can be manufactured at low cost. The device inaccordance with the invention meets all said requirements.

For the insulation material use can suitably be made of many materialsprovided they can be provided in the liquid state. Examples of suitablematerials are polymers, such as epoxy-like materials, polyacrylates,polyimides, but also ceramic materials such as silica, alumina andsimilar materials that are provided by means of sol-gel processing, andorganic materials such as benzocyclobutene. It is particularlyadvantageous to apply a thermally curable material since the cover isnot necessarily transparent. To preclude parasitic capacitances, use ispreferably made of a material having a low dielectric constant, such asan alkyl-substituted silica, HSQ, benzocyclobutene, SiLk.

It is a second object of the invention to provide a method of the typementioned in the opening paragraph, by means of which a semiconductordevice can be obtained that can be placed on a carrier by using bumps,and which method can be carried out for a large number of devices at thesame time.

The second object of the invention is achieved in that the methodcomprises the steps of:

-   -   providing the body with the semiconductor element and a cover,        which cover comprises a patterned layer of electroconductive        material and a sacrificial layer,    -   assembling the body and the cover in such a manner that the        contacts of the semiconductor element are connected to the        patterned layer of the cover    -   providing an envelope between the cover and the body, the        patterned layer being mechanically anchored in the envelope, and    -   removing the sacrificial layer from the cover.

The use of a sacrificial layer enables the manufacture to be simplifiedto predominantly the assembly of a cover and a body, after which theenvelope is provided. This process is very robust. If desirable,structural aligning means may be provided for aligning the cover and thebody. To interconnect the conductive layers in the cover and the bodyuse is made of a thermally conductive, known connection means such as ananisotropically conductive glue, a solder or metal bump, or the like.This has the additional advantage that the process can be carried outindependently of the specific shape of the cavity, the material of thebody or the constitution of the semiconductor element. What is paramountis that a good connection is established between the contacts of thesemiconductor element and the contact surfaces. At the same time thereis enough freedom of design and construction: firstly, the contactsurfaces can be locally provided, i.e. at the location of the contacts,with thickened portions to compensate for differences in height.Secondly, bumps can be applied that allow some play. Thirdly, theprocess can be applied on a large scale using standard elements. Thus,the design of the cavity can be adapted thereto.

The sacrificial layer chosen is a layer that forms a substrate for theconductive layer and that can be removed after assembly. For examplesilicon and aluminum are suitable materials which can be removed verywell by means of etching.

Oxides, such as alumina and silica are also suitable as well aspolyimides, acrylates and other condensation polymers. They are removed,for example, by means of etching, polishing or delaminating. Acombination of these techniques is also possible, which is particularlyfavorable if the sacrificial layer comprises a stack of layers. Anexample of such a stack is an Si—SiO₂—Si stack. The patterned layer hasa thickness of for instance 1 to 40 μm., preferably 5 to 15 μm. Thesacrificial layer has a thickness of for instance 25 to 75 μm.

In a first embodiment the body with the semiconductor element isprovided by:

-   -   providing the semiconductor element on a temporary carrier, the        contacts being at the side of the temporary carrier;    -   molding the semiconductor element, therewith forming the body of        electrically insulating material; and    -   removal of the temporary carrier, therewith providing the        aperture. This embodiment is particularly suitable for the        manufacture of multichip modules.

In a second embodiment the body with the semiconductor element isprovided with a thermally conductive layer at the inner side of thecavity, which is in thermal communication with the semiconductorelement, and wherein the body with the semiconductor element is providedby placing the semiconductor element on the thermally conductive layerof the body. This allows the manufacture of devices with good heatdissipation.

An alternative realization of this embodiment resides therein that thesemiconductor elements are not placed in the cavities of the body, butare place on the electrically conductive, patterned layer of the cover.This alternative realization is a method according to claim 10.

In a favorable embodiment, a patterned sub-layer is present in thecover, between the patterned layer and the sacrificial layer, whichpatterned layer and which sub-layer comprise a first and a secondpattern, which patterns are mutually separated by a recess having alarger diameter in the plane of the sub-layer than in the plane of thepatterned layer. In this manner, the patterned layer is directlymechanically anchored in the envelope: when the envelope is provided,the recesses are filled; by virtue of the larger diameter of the recessin the sub-layer, the envelope is present below, above and next to thepatterned layer. In this connection, it is favorable if the sub-layer ispatterned essentially according to the same mask as the patterned layer.What is different, however, is that, in a plane parallel to the firstside, the patterns in the sub-layer have a smaller diameter thancorresponding patterns in the patterned layer. It is favorable, inparticular, if the patterned layer serves as the etch mask for thesub-layer, and if a wet-chemical etching operation is carried out,resulting in the formation of an underetch.

The sub-layer may be part of the sacrificial layer. Alternatively, thesub-layer may comprise different materials. If the sub-layer is part ofthe sacrificial layer, the small diameter of the sub-layer is obtainedby an etching treatment in an etchant which is selective with respect tothe material of the patterned layer.

For the envelope use is preferably made of an insulating material. It isfavorable if the provision of the envelope does not only lead to thecontact surfaces being anchored in the envelope but also to thesemiconductor element being encapsulated by the envelope. The mechanicalanchoring is the result of patterns in the patterned conductive layer ofthe cover having a larger diameter than the corresponding patterns inthe underlying sub-layer. With respect to the sub-layer, the patterns inthe patterned layer have projecting edges which are anchored in theenvelope.

In a favorable embodiment, the body comprises a plurality of cavities.After semiconductor elements have been placed, the body is assembledwith a suitable cover. Only after the sacrificial layer has beenremoved, the assembly of body and cover is separated into individualelectronic devices.

In a further embodiment, the body comprises glass. The cavity is formedin this glass body by means of a blasting technique, after which athermally conductive layer is applied on the inner side of the cavity,which layer extends to beyond the cavity. A favorable example of ablasting technique is powder blasting, which is known per se to personsskilled in the art. The use of glass has the advantage that it providesfor very good insulation. In addition, glass is easy to process both inrespect of the formation of cavities and the separation of large glassplates into individual devices. Besides, by choosing the glass, thethermal conductivity thereof can be adjusted.

In a different embodiment, the body is provided by deforming a foil of athermally conductive layer and a sacrificial layer so as to form thecavity, the sacrificial layer being removed after the envelope has beenprovided between the body and the cover. In fact, the material used forthe body and for the cover is the same. In an additional step, the bodyis deformed. This deforming operation may be a folding operation. Toform a cavity, use is preferably made however of a mold for depressingthe foil. Good results have been achieved in this manner. The foildeformation process is described in greater detail in thenon-prepublished application EP 02078208.2 (PHNL020719), which isconsidered to be included herein by reference.

In a particularly advantageous modification of this embodiment, the bodyis provided with a protective coating, for example by molding using apolymer material, after the sacrificial layer has been removed. Theresultant device essentially comprises the semiconductor element, thecontact surfaces, the thermally conductive layer and the envelope. Thisdevice is very light and can be embodied so as to have small dimensions,while at the same time the heat-dissipating power is sufficient.

These and other aspects of the device and the method in accordance withthe invention are apparent from and will be elucidated with reference tothe embodiment(s) described hereinafter.

In the drawings:

FIG. 1 is a diagrammatic cross-sectional view of a first embodiment ofthe device;

FIGS. 2A-D are diagrammatic cross-sectional views of the body, the coverand the device in different stages of the method;

FIGS. 3A-H are diagrammatic cross-sectional views of the body and thecover in different stages of a second embodiment of the method,resulting in a second embodiment of the device.

The Figs. are not drawn to scale and some dimensions are exaggeratedstrongly for clarity. Corresponding regions or parts are indicated bymeans of the same reference numerals whenever possible.

FIG. 1 is a diagrammatic cross-sectional view of a first embodiment of adevice 100 in accordance with the invention. Said device 100 comprises abody 20, for example of glass, having a first side 21 and a second side22 facing away from said first side. The body 20 has a cavity 30 with anaperture 38 on the first side 21. This aperture 38 is closed by apatterned layer 45 and an envelope 35. The cavity 30 has an inner side39 wherein the bottom 31 of the cavity 30 is situated. The inner side 39of the cavity 30 is provided entirely, in this example, with a thermallyconductive layer 33 having a thickness between 5 and 50 μm, preferablyin the range from 10-25 μm. The thermally conductive layer 30 extends asfar as the end portions 34 on the first side 21 of the body 20. Thecavity 30 accommodates a semiconductor element 10, in this case abipolar transistor, with emitter and base contacts 11, 12, 13 on thefirst side 21 of the body 20 and a collector contact at the bottom 31 ofthe cavity 30. The transistor 10 is in thermal contact with thethermally conductive layer 33 via the bottom 31 of the cavity 30. Toattach the semiconductor element 10 to the bottom 31 of the cavity useis made of a conductive adhesive layer 14. The cavity is additionallyfilled with the envelope 35 in which also the patterned layer 45 ismechanically anchored. This patterned layer 45 having a thicknessranging preferably between 10 and 50 μm comprises contact surfaces 47,48. The contact surfaces 48 are in contact with the end portions 34 ofthe thermally conductive layer 33. The contact surfaces 47 are incontact with the contacts 11, 12, 13 of the transistor 10. In additionto contact surfaces 47, 48, the patterned layer 45 may compriseinterconnects by means of which the semiconductor element 10 isconnected to other elements in the device. For example, it is possiblethat the thermally conductive layer does not cover the entire innersurface of the cavity 30, but that contacts are present instead. Asuitably chosen connection of contact surfaces 47 and 48 then providesfor an interconnect to the first side 21 of the body 20. The patternedthermally conductive layer 33 can also suitably be used then as aninterconnect layer on which further elements are placed. If thesemiconductor element 10 is a field effect transistor, or anotherelement with all contacts on one side, the thermally conductive layer 33does not have to extend as far as the first side 21 of the body 20provided that another way of heat dissipation has been realized, forexample via heat conductors in the body 20 or via a thermally conductiveconnection, such as a metal connection from the bottom 31 of the cavity30 to the second side 22 of the device 100.

FIG. 2 shows several stages in the manufacture of the device 100 shownin FIG. 1. The body 20 shown in FIG. 2A and the cover 40 shown in FIG.2B are used as the starting elements.

FIG. 2A shows the body 20 prior to assembly. The body 20 comprises glassand is provided with cavities 30 at the level of the board by means ofpowder blasting. The aperture 38 of the cavity 30 is present on thefirst side 21 of the body 20. The process of forming such cavities 30 inbodies 20 is known per se and is used, for example, for display screenson the basis of polymeric light-emitting diodes. The depth of the cavity30 is adapted to the height of the semiconductor element 10 to beplaced. After the formation of the cavities 30, the thermally conductivelayer 33 of copper is deposited by means of sputtering via a mask. Thethermally conductive layer can also be patterned in a photolithographicprocess, in particular, if this is the last step in the manufacturingprocess, i.e. when the cavity is filled. The photoresist that is neededfor the photographic patterning and which is applied by spincoating,will then be spread over the first side. After the thermally conductivelayer 33 has been applied, the semiconductor element 10 is placed, saidsemiconductor element being provided with an adhesive layer 14. Next,the semiconductor element 10 is provided with solder or metal bumps atthe contacts 11, 12, 13 and at the ends of the thermally conductivelayer 33. For the solder material use is made of, for example, PbSn.

FIG. 2B shows the cover 40 prior to assembly. In this example, which isnot essential, the cover 40 has a first side 41 and a second side 42, apatterned layer 45 being applied to the first side 41 and a sacrificiallayer 44 being applied to the second side 42. A sub-layer 46 is incontact with the patterned layer 45, which sub-layer is part of thesacrificial layer 44, in this embodiment. Here, the sacrificial layer 44is an approximately 60 μm thick aluminum layer. The patterned layer 45comprises copper and has a thickness of approximately 10 μm. Thepatterned layer 45 and the sub-layer 46 comprise patterns 47 betweenwhich there is a recess 461. This recess 461 has a larger diameter inthe plane of the sub-layer 46 than in the plane of the patterned layer45.

The cover 40 is manufactured as follows: a halter-shaped mask of silicondioxide is formed by means of photolithography on the patterned layer45, after which the copper of the patterned layer 45 is removed outsidesaid mask by means of etching using an aqueous solution of ferricchloride. In this process, a recess 461 is formed in the cover 40. Bymeans of said recess 461 contact surfaces 47, 48 are defined. Another,selective etchant is subsequently used to remove part of the sacrificiallayer 44. In this process, underetching of the sacrificial layer 44occurs relative to the patterned layer 45, thereby forming the sub-layer46. For example caustic soda can be used as the selective etchant foraluminum.

FIG. 2C shows the device 100 after assembly of the cover 40 and the body20. The body 20 and the cover 40 are aligned by means of mechanicalaligning means provided in the patterned layer 45 of the cover and inthe thermally conductive layer 33 on the first side 21 of the body 20.Alternatively, for example, light can be used for said alignment. Toobtain a sufficiently sealing connection between the patterned layer 45and the thermally conductive layer 33, a thermal treatment is carriedout at approximately 200° C.

It is noted that it is alternatively possible to place the semiconductorelement 10 on the cover 40, after which assembly takes place.Particularly in said case, various interconnection techniques, such assolder, conductive adhesive, metal bumps, diffusion connection, can beused to interconnect the contacts 11, 12, 13 and the contact surfaces 47on the one hand, and the ends of the thermally conductive layer 33 andthe contact surfaces 48 on the other hand. Instead of solder, metalbumps can be used as the connection means between the contacts of thebody 20 and the contact surfaces 47, 48 of the cover. In said case, itis generally required however to apply an adhesive layer to the copper,for example a layer of Au, Ag, Pd and/or Ni and, preferably, to thethermally conductive layer 33 as well as to the patterned layer 45. Forthe bumps use can be made of, inter alia, Au and alloys of Au, such asAu-Sn. The use of Au-Sn is very favorable in combination with anacrylate layer, as described in the non-prepublished application EP02077228.1 (NL020471).

FIG. 2D shows the device 100 after the envelope 35 of insulatingmaterial has been provided in the cavity 30. In this example, an epoxyis used as the insulating material. Capillary forces, if necessaryfollowed by a vacuum treatment, make sure that the epoxy also fills therecesses 461. After said filling process, an additional heating step iscarried out to cure the insulating material.

FIG. 2E finally shows the device 100 after the sacrificial layer 44 hasbeen removed. Said layer is removed, in this example, by etching usingcaustic soda. In fact, the device 100 is ready now. Next, bumps can beprovided on the contact surfaces 47, 48. If the device 100 has beenmanufactured at the level of the board, the body 20 is first separatedinto individual devices. To simplify this separation process, thepatterned layer 45 and the thermally conductive layer 33 are patternedsuch that they are absent at the location of the sawing paths.Alternatively, also additional layers can be provided on the contactsurfaces 47, 48.

FIGS. 3A-H show a second embodiment of the method of manufacturing thedevice 100. They show in diagrammatic cross-sectional views variousstages in the manufacturing process. In fact, the method is carried outin the same manner as the method described with reference to FIGS. 2A-E.The difference between the methods resides in that for the body 20 withthe thermally conductive layer 33 use is made of a foil that isessentially identical to the foil used as a cover. In this application,the foil must be deformed first. At a later stage, the sacrificial layerof the foil can be substituted with an insulating layer. As a result,the device can remain limited to a thermally conductive layer 33 and asemiconductor element 10 which are encapsulated in the enveloping layers35, 25, while all contact surfaces 47, 48 are situated on the first side21 of the device 100. This has the advantage that the device 100 is verylight and can be manufactured on a small scale.

FIGS. 3A-C show three steps in the manufacture of the body 20 prior toassembly. A foil 50 with the thermally conductive layer 33 and asacrificial layer 36 are used as the starting elements. After thethermally conductive layer 33 has been patterned, if necessary, inaccordance with a desired pattern, the foil 50 is formed. For thispurpose, a mold is brought into contact with the foil 50, the foil beingpresent on a hard substrate (which may be part of the mold). The mold isprovided with a desired pattern, such that the cavity 30 is realized.The mold is, for example, a Si substrate with Ni bumps in the desiredpattern thereon. The mold may be situated on either side of the foil 50;in other words, the pattern in the mold may be the positive of thecavity 30 or the negative of said cavity.

FIG. 3D shows the cover 40. FIG. 3E shows the assembled device 100. FIG.3F shows the device 100 after the envelope 35 has been provided. Thesesteps are identical to the steps discussed with reference to the FIGS.2B-2D.

FIG. 3G shows the device 100 after the sacrificial layers 44 and 36 havebeen removed. When the device 100 is immersed in an etch bath, this cantake place in a single step. Of course, the sacrificial layers may becomposed of a different material, in which case two etch baths are used.If the sacrificial layer 36 is of an insulating material or if the onlypatterns provided in the thermally conductive layer 33 are theconnection from the bottom 31 of the cavity 30 to the first side 21 ofthe body, it is not necessary to remove the sacrificial layer 36.

FIG. 3H shows the device 100 after a further envelope 25 has beenprovided, and after solder 60 has been provided on the contact surfaces47, 48.

1. An electronic device having a body having a cavity with an inner sideand an aperture a semiconductor element provided with contacts, whichsemiconductor element is present in the cavity and at least part of itscontacts are situated at the aperture of the cavity; characterized inthat the contacts are in electric contact, via conductive connectingpieces, with contact surfaces, which contact surfaces are anchored inelectrically insulating material.
 2. An electronic device as claimed inclaim 1, wherein the body comprises an electrically insulating materialwhich encapsulates the semiconductor element with the exclusion of theaperture.
 3. An electronic device as claimed in claim 1, wherein theelectrically insulating material forms an envelope, which also fills thecavity.
 4. An electronic device as claimed in claim 3, furthercomprising a thermally conductive layer which is in thermalcommunication with the semiconductor element and is at least partlysituated on the inner side of the cavity.
 5. An electronic device asclaimed in claim 4, characterized in that the body is a multilayersubstrate of insulating material with conductive intermediate layers,the thermally conductive layer being part of an intermediate layer ofthe multilayer substrate.
 6. An electronic device as claimed in claim 1,characterized in that further components are present, which areconnected, as desired with the contacts of the semiconductor element byelectroconductive interconnects.
 7. A method of manufacturing anelectronic device comprising a body having a cavity with an inner sideand an aperture, and a semiconductor element provided with contacts,which semiconductor element is present in the cavity and at least partof its contacts are situated at the aperture of the cavity; which methodcomprises the steps of: providing the body with the semiconductorelement and a cover, which cover comprises a patterned layer ofelectroconductive material and a sacrificial layer, assembling the bodyand the cover in such a manner that the contacts of the semiconductorelement are connected to the patterned layer of the cover providing anenvelope between the cover and the body, the patterned layer beingmechanically anchored in the envelope, and removing the sacrificiallayer from the cover.
 8. A method as claimed in claim 7, wherein thebody with the semiconductor element is provided by: providing thesemiconductor element on a temporary carrier, the contacts being at theside of the temporary carrier; molding the semiconductor element,therewith forming the body of electrically insulating material; andremoval of the temporary carrier, therewith providing the aperture.
 9. Amethod as claimed in claim 7, wherein the body is provided with athermally conductive layer at the inner side of the cavity, which is inthermal communication with the semiconductor element, and wherein thebody with the semiconductor element is provided by placing thesemiconductor element on the thermally conductive layer of the body. 10.A method of manufacturing an electronic device comprising a body havinga cavity with an inner side and an aperture, and a semiconductor elementprovided with contacts, which semiconductor element is present in thecavity and at least part of its contacts are situated at the aperture ofthe cavity; which method comprises the steps of: providing the body anda cover, at least a part of the inner side of the cavity being providedwith a thermally conductive layer, and said cover comprises a patternedlayer of electroconductive material and a sacrificial layer, placing thesemiconductor element on the patterned layer of the cover; assemblingthe body and the cover in such a manner that the semiconductor elementis in thermal communication with the thermally conductive layer, andthat contacts of the semiconductor elements are connected to thepatterned layer of the cover; providing an envelope between the coverand the body, the patterned layer being mechanically anchored in theenvelope, and removing the sacrificial layer from the cover.
 11. Amethod as claimed in claim 8, characterized in that a patternedsub-layer is present in the cover, between the patterned layer and thesacrificial layer, which patterned layer and which sub-layer comprise afirst and a second pattern, which patterns are mutually separated by arecess having a larger diameter in the plane of the sub-layer than inthe plane of the patterned layer.
 12. A method as claimed in claim 8,characterized in that the body comprises a plurality of cavities and isassembled with a suitable cover after placement of semiconductorelements and that after removal of the sacrificial layer, the assemblyof body and cover is separated into individual electronic devices.
 13. Amethod as claimed in claim 9, characterized in that the body comprisesglass, and the cavity is formed by means of a blasting technique, afterwhich a thermally conductive layer is applied on the inner side of thecavity, which layer extends to beyond the cavity.
 14. A method asclaimed in claim 9, characterized in that the body is provided bydeforming a foil of a thermally conductive layer and a sacrificial layerso as to form the cavity, the sacrificial layer being removed after theenvelope has been provided between the body and the cover.